(1) Field of the Invention
The present invention relates to an element wire made of metal, at least one said element wire being coated with an electrically insulating coating so as to constitute an electric wire, an electric wire including the element wire or the element wires, and a process for producing an element wire.
(2) Description of the Related Art
Generally, a motor vehicle as a mobile unit mounts various electronic equipment, for example, a lamp such as a headlamp or tail lamp, a motor such as a starter motor or motor for an air conditioner, and so on.
In order to supply electric power to the various electronic equipment described above, the motor vehicle is provided with a wiring harness. The wiring harness includes a plurality of electric wires. The electric wire includes an electrically conductive core wire and an electrically insulating coating which coats the core wire. The core wire includes a plurality of element wires. The element wire is made of electrically conductive metal such as copper. The element wire is formed long having a round shape in section.
The element wire described above can be obtained by subjecting an electrically conductive material to rolling or drawing. Therefore, even if a crystal grain of the element wire is an isometric grain before drawing of the element wire, the crystal grain of the element wire becomes an elongated grain after the drawing. Generally, a core wire consisting of element wires, a crystal grain of which is an elongated grain, tends to deteriorates in terms of its ductility, that is, tends to be easily broken under tension. Therefore, when the element wire, a crystal grain of which is an elongated grain, becomes thin as the electric wire constituting the wiring harness becomes thin, the element wire constituting the core wire of the electric wire tends to be easily broken upon mounting of the wiring harness on a motor vehicle and therefore, handling of the wiring harness requires particular caution to a worker.
It is possible to make a crystal grain of the element wire be an isometric grain by subjecting the element wire, a crystal grain of which is an elongated grain, to a heat treatment. However, in this case, the crystal grain grows excessively, causing a problem that mechanical strength of the core wire is deteriorated although the ductility of the core wire is improved. Alternatively, it is possible to make a crystal grain of the element wire be a fine isometric grain by subjecting the element wire, a crystal grain of which is an elongated grain, to deposition so as to generate a second phase. However, in this case, addition of an another element and a deposition processing by heating are required, causing a cost-up for producing the electric wire due to an increase in required man-hour.